diff --git a/obmc/mapper/server.py b/obmc/mapper/server.py
index 0120de5..a9afee6 100644
--- a/obmc/mapper/server.py
+++ b/obmc/mapper/server.py
@@ -27,6 +27,14 @@
 import obmc.dbuslib.enums
 
 
+class MapperBusyException(dbus.exceptions.DBusException):
+    _dbus_error_name = 'org.freedesktop.DBus.Error.ObjectPathInUse'
+
+    def __init__(self):
+        super(MapperBusyException, self).__init__(
+            'busy processing bus traffic')
+
+
 class MapperNotFoundException(dbus.exceptions.DBusException):
     _dbus_error_name = obmc.mapper.MAPPER_NOT_FOUND
 
@@ -219,6 +227,7 @@
         self.manager = Manager(bus, obmc.dbuslib.bindings.OBJ_PREFIX)
         self.unique = bus.get_unique_name()
         self.bus_map = {}
+        self.defer_signals = {}
         self.bus_map[self.unique] = obmc.mapper.MAPPER_NAME
 
         # add my object mananger instance
@@ -254,6 +263,19 @@
         self.service = dbus.service.BusName(
             obmc.mapper.MAPPER_NAME, self.bus)
 
+    def discovery_callback(self, owner, items):
+        if owner in self.defer_signals:
+            self.add_items(owner, items)
+            pending = self.defer_signals[owner]
+            del self.defer_signals[owner]
+
+            for x in pending:
+                x()
+
+    def discovery_error(self, owner, path, e):
+        if owner in self.defer_signals:
+            raise e
+
     def cache_get(self, path):
         cache_entry = self.cache.get(path, {})
         if cache_entry is None:
@@ -270,28 +292,47 @@
         new = list(set(old).union([dbus.BUS_DAEMON_IFACE + '.ObjectManager']))
         self.update_interfaces(path, owner, old, new)
 
+    def defer_signal(self, owner, callback):
+        self.defer_signals.setdefault(owner, []).append(callback)
+
     def interfaces_added_handler(self, path, iprops, **kw):
         path = str(path)
         owner = str(kw['sender'])
         interfaces = self.get_signal_interfaces(owner, iprops.iterkeys())
-        if interfaces:
+        if not interfaces:
+            return
+
+        if owner not in self.defer_signals:
             self.add_new_objmgr(str(kw['sender_path']), owner)
             cache_entry = self.cache_get(path)
             old = self.interfaces_get(cache_entry, owner)
             new = list(set(interfaces).union(old))
             new = {x: iprops[x] for x in new}
             self.update_interfaces(path, owner, old, new)
+        else:
+            self.defer_signal(
+                owner,
+                lambda: self.interfaces_added_handler(
+                    path, iprops, **kw))
 
     def interfaces_removed_handler(self, path, interfaces, **kw):
         path = str(path)
         owner = str(kw['sender'])
         interfaces = self.get_signal_interfaces(owner, interfaces)
-        if interfaces:
+        if not interfaces:
+            return
+
+        if owner not in self.defer_signals:
             self.add_new_objmgr(str(kw['sender_path']), owner)
             cache_entry = self.cache_get(path)
             old = self.interfaces_get(cache_entry, owner)
             new = list(set(old).difference(interfaces))
             self.update_interfaces(path, owner, old, new)
+        else:
+            self.defer_signal(
+                owner,
+                lambda: self.interfaces_removed_handler(
+                    path, interfaces, **kw))
 
     def properties_changed_handler(self, interface, new, old, **kw):
         owner = str(kw['sender'])
@@ -303,12 +344,18 @@
         if associations is None:
             return
 
-        associations = [
-            (str(x), str(y), str(z)) for x, y, z in associations]
-        self.update_associations(
-            path, owner,
-            self.index_get_associations(path, [owner]),
-            associations)
+        if owner not in self.defer_signals:
+            associations = [
+                (str(x), str(y), str(z)) for x, y, z in associations]
+            self.update_associations(
+                path, owner,
+                self.index_get_associations(path, [owner]),
+                associations)
+        else:
+            self.defer_signal(
+                owner,
+                lambda: self.properties_changed_handler(
+                    interface, new, old, **kw))
 
     def process_new_owner(self, owned_name, owner):
         # unique name
@@ -337,6 +384,11 @@
         if valid and new:
             self.process_new_owner(owned_name, new)
         if valid and old:
+            # discard any unhandled signals
+            # or in progress discovery
+            if old in self.defer_signals:
+                del self.defer_signals[old]
+
             self.process_old_owner(owned_name, old)
 
     def update_interfaces(self, path, owner, old, new):
@@ -444,6 +496,9 @@
 
     @dbus.service.method(obmc.mapper.MAPPER_IFACE, 's', 'a{sas}')
     def GetObject(self, path):
+        if len(self.defer_signals):
+            raise MapperBusyException()
+
         o = self.cache_get(path)
         if not o:
             raise MapperNotFoundException(path)
@@ -451,6 +506,9 @@
 
     @dbus.service.method(obmc.mapper.MAPPER_IFACE, 'si', 'as')
     def GetSubTreePaths(self, path, depth):
+        if len(self.defer_signals):
+            raise MapperBusyException()
+
         try:
             return self.cache.iterkeys(path, depth)
         except KeyError:
@@ -458,6 +516,9 @@
 
     @dbus.service.method(obmc.mapper.MAPPER_IFACE, 'si', 'a{sa{sas}}')
     def GetSubTree(self, path, depth):
+        if len(self.defer_signals):
+            raise MapperBusyException()
+
         try:
             return {x: y for x, y in self.cache.dataitems(path, depth)}
         except KeyError:
@@ -601,6 +662,9 @@
 
     @dbus.service.method(obmc.mapper.MAPPER_IFACE, 's', 'a{sa{sas}}')
     def GetAncestors(self, path):
+        if len(self.defer_signals):
+            raise MapperBusyException()
+
         elements = filter(bool, path.split('/'))
         paths = []
         objs = {}